The present invention relates to thermoprocessable flexible fluorinated polymers.
More specifically the present invention relates to flexible copolymers of ethylene/tetrafluoroethylene (ETFE) and ethylene/chlorotrifluoroethylene (ECTFE), modified with hydrogenated monomers. Said copolymers are used for obtaining sheets, pipes, and manufactured articles, among which flexible cables, i.e. having a low elastic modulus, are preferred. More specifically, for the application of flexible cables, said copolymers must not show a necking at yield on the stress-strain curve, thus avoiding the whitening effect on the bent cable. The whitening effect visually represents the material plastic deformation wherefore this cannot recover any longer the initial state.
Ethylene/tetrafluoroethylene (ETFE) and ethylene/chlorotrifluoroethylene (ECTFE) (co)polymers modified with hydrogenated monomers to which flexibility (low elastic modulus) is conferred by addition of hydrogenated plasticizers, are known in the prior art.
One disadvantage of these plasticized (co)polymers when used in the chemical process industry (CPI) is that the plasticizers can migrate from the polymer polluting the process fluids and reducing the manufactured article flexibility.
In the case of the wire and cable applications, for safety reasons these flexible cables must show a high time to ignition, a low smoke and heat releases when they are subjected to a heat source such as for example in the cone calorimeter (see ASTM E1354 test). However the presence of plasticizers increases the release of smoke and heat when the manufactured article comes into direct contact with the flame. Besides, the presence of plasticizers increases the polymer dielectric constant, which is undesired for cables.
The need was therefore felt to have available flexible ethylene/tetrafluoroethylene (ETFE) and ethylene/chlorotrifluoroethylene (ECTFE) (co)polymers not plasticized.
An object of the present invention is therefore a composition comprising a polymer mixture A of polymers formed by moles:
(a) from 10 to 70%, preferably from 35 to 55%, of ethylene (E),
(b) from 30 to 90%, preferably from 45 to 65%, of a fluorinated monomer selected from tetrafluoroethylene (TFE), chlorotrifluoroethylene (CTFE), or mixtures thereof,
(c) from 0.1 to 30%, preferably from 1 to 15%, with respect to the total amount of monomers (a) and (b), of one or more acrylic monomers of formula:
CH2xe2x95x90CHxe2x80x94COxe2x80x94Oxe2x80x94R2xe2x80x83xe2x80x83(I) 
xe2x80x83wherein R2 is a linear and/or branched alkyl radical, C1-C20, from 1 to 20 carbon atoms, or cycloalkyl from 3 to 20 carbon atoms, or R2 is H; the R2 radical can optionally contain: heteroatoms preferably Cl, O, N; one or more functional groups preferably selected from OH, COOH, epoxide, ester and ether; and double bonds;
characterized in that the polymer mixture A comprises polymer fractions having a different content of the comonomer of formula (I) such that the elastic modulus at 23xc2x0 C. (ASTM D1708) of said polymer mixture A is lower than at least 10% of the elastic modulus of a polymer formed by monomers a), b) and c) wherein the polymer fractions have substantially an equal content of the comonomer of formula (I).
The polymer mixture A of the composition of the invention is obtainable by blend. For example at least two polymers A1 and A2 can be mixed comprising the monomers of the invention wherein the comonomer of formula (I) in the copolymer A2 is at least 1.5 times the amount of comonomer of formula (I) in the copolymer A1. The ratio by weight between the copolymers A1/A2 is preferably comprised between 1/9 and 9/1.
Preferably the amount of comonomer of formula (I) in the copolymer A2 is at least 1.75 times the amount of comonomer of formula (I) in the copolymer A1, the ratio by weight between the copolymers A1/A2 being preferably comprised between 1/4 and 4/1.
Still more preferably the composition is characterized in that the amount of comonomer of formula (I) in the copolymer A2 is at least twice the amount of comonomer of formula (I) in the copolymer A1, the ratio by weight between the copolymers A1/A2 being preferably between 3/7 and 7/3.
The blends can directly be obtained in polymerization or by physical mixing. Indeed, the polymer mixture A can be obtained by the synthesis in sequence of the polymer fractions in a single polymerization of the above mentioned monomers a), b) and c).
The acrylic monomers of formula (I) are selected from ethylacrylate, n-butylacrylate, acrylic acid, hydroxyethylacrylate, hydroxypropylacrylate, (hydroxy)ethylhexylacrylate.
Preferably the monomer of formula (I) is n-butyl acrylate.
Preferably the fluorinated monomer b) is chlorotrifluoroethylene (CTFE).
Another object of the present invention is the preparation of the polymer mixture A in polymerization, in which in a conversion range of ethylene equal to 50%, at least 75% by weight of the total amount of the comonomer of formula (I) is added to the reaction medium.
Preferably the process is characterized in that in a conversion range of ethylene equal to 30%, at least 50% by weight of the total amount of the comonomer of formula (I) is added to the reaction medium.
Furthermore preferably after 90% of ethylene conversion, less than 7% by weight of the total amount of the comonomer of formula (I) is added to the reaction medium.
Furthermore still more preferably after 80% of ethylene conversion, less than 7% by weight of the total amount of the comonomer of formula (I) is added to the reaction medium.
This preparation process of the polymer mixture A is a copolymerization of the corresponding monomers in the presence of radical initiators, in suspension in organic medium, in the presence or absence of water, or in aqueous emulsion, at a temperature in the range between xe2x88x9260xc2x0 and 150xc2x0 C., preferably between xe2x88x9220xc2x0 and 100xc2x0 C., more preferably between xe2x88x9210xc2x0 and 50xc2x0 C., and pressures in the range 0.5-100 bar, preferably 5-40 bar.
Among the radical initiators, that can be in particular used are:
(i) bis-acylperoxides of formula (Rfxe2x80x94COxe2x80x94O)2, wherein Rf is a (per)haloalkyl C1-C10 (see for example EP 185,242 and U.S. Pat. No. 4,513,129), or a perfluoropolyoxyalkylene group (see for example EP 186,215 and U.S. Pat. No. 5,021,516); among them, bis-trichloroacetylperoxide and bis-dichlorofluoroacetylperoxide are particularly preferred (see U.S. Pat. No. 5,569,728);
(ii) dialkylperoxides of formula (RHxe2x80x94O)2, wherein RH is an alkyl C1-C10; diterbutylperoxide (DTBP) is particularly preferred;
(iii) hydrosoluble inorganic peroxides, such as ammonium or alkaline metal persulphates or perphosphates; sodium and potassium persulphates are particularly preferred.
(iv) dialkylperoxydicarbonates, wherein the alkyl has from 1 to 8 carbon atoms, such as for example di-n-propyl-peroxydicarbonate and di-isopropyl-peroxydicarbonate (see EP 526,216);
(v) organic or inorganic redox systems, such as ammonium persulphate/sodium sulphite, hydrogen peroxide/aminoiminomethansulphinic acid, terbutylhydroperoxide/metabisulphite (see U.S. Pat. No. 5,453,477).
The molecular weight control of the polymer mixture A can be made by using the telogen activity of the comonomers of formula (I) comparable to that of a conventional chain transfer agent especially at high temperatures, i.e. in the range 20xc2x0-100xc2x0 C., or by using specific chain transfer agents. Among these it can be mentioned: ketones, esters, ethers or aliphatic alcohols having from 3 to 10 carbon atoms; hydrocarbons or halogenated hydrocarbons, having from 1 to 6 carbon atoms; bis(alkyl)carbonates wherein the alkyl has from 1 to 5 carbon atoms; etc. Among them, chloroform and alkyl substituted cyclopentanes, in particular methylcyclopentane, are particularly preferred (see U.S. Pat. No. 5,510,435). The transfer agent is fed to the reactor at the beginning of the reaction, or in a continuous way or batchwise during the polymerization. The amount of the used chain transfer agent can range within rather wide limits, depending on the type of the used monomers, the reaction temperature and the molecular weight requested. Generally, said amount ranges between 0.01 and 30% by weight, preferably between 0.05 and 10% by weight, with respect to the total amount of the monomers fed into the reactor.
The process in aqueous emulsion is carried out in the presence of one or more fluorinated surfactants, among which the most commonly used are those of general formula:
Rfxe2x80x94Xxe2x88x92M+
wherein Rf is a (per)fluoroalkyl chain C5-C16 or a (per)fluoropolyoxyalkylene chain, Xxe2x88x92 is xe2x80x94COOxe2x88x92 or xe2x80x94So3xe2x88x92, M+ is selected from: H+, NH4+, an alkaline metal ion. Among them we mention: ammonium and/or sodium perfluoro-octanoate, (per)fluoropolyoxyalkylenes ended with one or more carboxylic groups, etc.
The process in emulsion can be advantageously carried out in the presence of dispersions, emulsions or microemulsions preferably of perfluoropolyoxyalkylenes, according to U.S. Pat. No. 4,789,717 and U.S. Pat. No. 4,864,006, or also of microemulsions of fluoropolyoxyalkylenes having hydrogenated end groups and/or hydrogenated repeating units, according to U.S. Pat. No. 5,498,680 in the name of the Applicant.
It has been found by the Applicant that the preparing process of the polymer mixture A in organic suspension in the presence of water leads to a product that tends to agglomerate making difficult the polymer discharge from the autoclave. Besides, the drying temperature between 100xc2x0 and 150xc2x0 C. of the so obtained polymer mixture A, i.e. its post-treatment, cannot be carried out in the conventional plants used for thermoplastic materials, due to the rubber-like behaviour of the polymer mixture A.
It has been surprisingly found by the Applicant a process for preparing the polymer mixture A in organic suspension in the presence of water and of a semicrystalline (co)polymer of the chlorotrifluoroethylene (PCTFE) containing at least 99% by moles of chlorotrifluoroethylene, the complement to 100 being one or more acrylic monomers or fluorinated monomers, these preferably selected from (per)fluoroalkylvinylethers, (per)fluorodioxoles, which allow to obviate the above mentioned drawbacks.
Said PCTFE can be added under the form of powder or latex which coagulates by adding a coagulant in the reaction medium in the presence of the organic and aqueous phase. The coagulating agents of PCTFE are those known in the coagulation of the fluoropolymer latexes, for example aluminum sulphate, nitric acid, hydrochloric acid, calcium chloride. Calcium chloride is preferred. The amount of the coagulants depends on the type of the used coagulant. Amounts in the range 0.001%-30% by weight with respect to the total amount of water in the reaction medium, preferably in the range 0.01%-5% by weight, can be used.
The PCTFE addition under the form of latex at the beginning and/or during the synthesis of the polymer mixture A is preferred. In particular in the addition during the synthesis of the polymer mixture A, the PCTFE latex amount can be suitably fed during the comonomer feeding of formula (I). Preferably the fed PCTFE amount is directly proportional to the fed amount of the comonomer of formula (I).
The PCTFE latex can be obtained by (co)polymerization in aqueous emulsion where the presence of a suitable surfactant is required. The fluorinated surfactants of formula:
xe2x80x83Rfxe2x80x94Xxe2x88x92M+
are the most commonly used, wherein Rf is a (per)fluoroalkyl chain C5-C16 or a (per)fluoropolyoxyalkylene chain, Xxe2x88x92 is xe2x80x94COOxe2x88x92 or xe2x80x94SO3xe2x88x92, M+ is selected from: H+, an alkaline metal ion. Among them we mention: sodium perfluoro-octanoate, (per)fluoropolyoxyalkylenes ended with one or more carboxylic groups, etc.
The process for obtaining the PCTFE latex can be advantageously carried out in the presence of dispersions, emulsions or microemulsions preferably of perfluoropolyoxyalkylenes, according to U.S. Pat. No. 4,789,717 and U.S. Pat. No. 4,864,006, or also of microemulsions of fluoropolyoxyalkylenes having hydrogenated end groups and/or hydrogenated repeating units, according to U.S. Pat. No. 5,498,680.
The preferred process for obtaining the PCTFE latex is characterized by the use of perfluoropolyoxyalkylenes microemulsion according to the European patent application EP 1,067,146 in the name of the Applicant herein incorporated by reference.
In the case of the PCTFE copolymerization in suspension, the reaction medium is formed by an organic phase, to which water is added in order to favour the heat dispersion developed during the reaction. The organic phase can be formed by the monomers themselves, without addition of solvents, or by the monomers dissolved in a suitable organic solvent. Among the solvents we can mention chlorofluorocarbons, such as CCl2F2 (CFC-12), CCl3F (CFC-11), CCl2FCClF2 (CFC-113), CClF2CClF2 (CFC-114), etc. Since said products have a destroying effect on the ozone present in the stratosphere, alternative products, such as the compounds containing only carbon, fluorine, hydrogen, and optionally oxygen, described in U.S. Pat. No. 5,182,342, have recently been suggested. In particular (per)fluoropolyethers with at least one hydrogenated end group, preferably two, of the xe2x80x94CF2H, xe2x80x94CF2CF2H, xe2x80x94CF(CF3)H type can be used.
As said above, in the synthesis in suspension of the polymer mixture A, optionally in the presence of PCTFE, the reaction medium is formed by an organic phase, to which water is added in order to favour the heat dispersion developed during the reaction. The organic phase can be formed by the monomers themselves, without addition of solvents, or by the monomers dissolved in a suitable organic solvent. Among the solvents we can mention branched chain hydrocarbons described in U.S. Pat. No. 5,434,229, having from 6 to 25 carbon atoms and a ratio between methyl groups and the number of carbon atoms higher than 0.5, such as for example 2,3-dimethylbutane, 2,3-dimethylpentane, 2,2,4-trimethylpentane, 2,2,4,6,6-pentamethylheptane, 2,2,4,4,6-pentamethylheptane, etc., or mixtures thereof. Other conventionally used organic solvents are chlorofluorocarbons, such as CCl2F2 (CFC-12), CCl3F (CFC-11), CCl2FCClF2 (CFC-113), CClF2CClF2 (CFC-114), etc. Since said products have a destroying effect on the ozone present in the stratosphere, alternative products, such as the compounds containing only carbon, fluorine, hydrogen, and optionally oxygen, described in U.S. Pat. No. 5,182,342, have recently been suggested. In particular (per)fluoropolyethers with at least one hydrogenated end group, preferably two, of the xe2x80x94CF2H, xe2x80x94CF2CF2H, xe2x80x94CF(CF3)H type can be used.
The synthesis process of the polymer mixture A in organic suspension in the presence of water and PCTFE leads to obtain a composition comprising from 1% to 75% by weight of PCTFE and from 25% to 99% by weight of the polymer mixture A. Preferably the polymer mixture A is in the range 70-95% by weight of the composition. More preferably the polymer mixture A is in the range 80-90% by weight of the composition.
As said with PCTFE a semicrystalline chlorotrifluoroethylene (co)polymer is meant, containing at least 99% by moles of chlorotrifluoroethylene, being the complement to 100 one or more acrylic or fluorinated monomers. The preferred fluorinated monomers are selected from perfluoroalkylvinylethers, perfluorodioxoles, preferably PCTFE is the CTFE homopolymer. The PCTFE having a Melt Flow Index (MFI) higher than 0.1 g/10xe2x80x2 measured at 265xc2x0 C. and at 10 kg load according to the ASTM D 1238-88 method is still more preferred.
As said the compositions of the present invention show an improved flexibility since they show elastic modulus values lower than those obtained in the prior art at equal content of comonomer of formula (I) uniformly distributed in the polymer.
In summary, this high flexibility of the composition of the present invention not imparted by plasticizers represents a remarkable advantage in the wire and cable industry (e.g. jaketing cables) (better dielectric properties and lower smoke release polymers) and in the CPI industry (e.g. sheets and pipes (permanent flexibility and no contamination of the process fluid).
Some embodiment Examples of the present invention are hereinafter reported, the purpose of which is merely illustrative but not limitative of the scope of the invention itself.